How do I find the mass of the second object if they both completely stop?

Question

A 1,272 kg truck going 15.2 m/s collides head on with a car going 26.4 m/s. If they both completely stop from the collision, what must the mass of the car be?

Answer 1

m₁v₁ - m₂v₂ = 0; v₂ = m₁v₁/m₂ = 1272kg·15.2m/s/26.4m/s = 732.36 kg